UAHuntsville Materials Science Faculty Research SymposiumDecember 05, 2012

Mark W. Lin, Ph.D.Associate Professor

Department of Mechanical and Aerospace EngineeringUniversity of Alabama in Huntsville

Huntsville, Alabama

Smart Materials Research at UAHuntsville

Boeing Seminar-2

Outline

Introduction Electrical Time Domain Reflectometry (ETDR) Distributed Strain Sensor

Impedance-Based Piezoelectric Sensor Hybrid Linear/Rotary Actuator

Shape Memory Alloy (Nitinol) Active Actuator

FEA Structural Analyses

Closing Thought

Boeing Seminar-3

Smart Structures

SKELETON composite/structural materials

MUSCULAR SYSTEM piezoelectric ceramics, piezoelectric polymers, shape memory alloys

SENSORY SYSTEM optical fiber sensors, piezoelectric polymer sensors, ETDR distributed strain sensors

MOTOR CONTROL SYSTEM modern distributed control algorithms

Boeing Seminar-4

Engineering Applications

Boeing Seminar-5

Smart Structures Design Philosophy

The material/structural systems can sense a need, can change based upon theneed, and can correct a mistake

Engineers will not have to learn from structural failures, but will be able tolearn from the “life experiences” of the structure.

Boeing Seminar-6

Discrete vs. Distributed Strain Sensing

Well-developed sensors currently available, such as strain gages, LVDT displacement sensors, piezoelectric transducers, Eddy current sensor, etc.

Acquiring data only at the points of interest

At the location where no sensor is present, direct measurements are not available

In practice, sensors are strategically placed at critical locations, and a mechanics-based model is used to subsequently approximate the structural response at other locations, if such data are needed

Discrete/Point Strain SensingDistributed Strain Sensing

Capable of measuring the needed data along the sensing line for the entire structure.

Having a potential to monitor integrity condition of an in-service structure, since structural failure can occur at any location.

Distributed Strain Sensors Currently Being Studied

Fiber optic sensor using Bragg grating method (quasi distributed)

Fiber optic sensor using Brillouin scattering method (true distributed, low spatial resolution, >4in)

Electrical time domain reflectometry (ETDR) strain sensor (true distributed, high spatial resolution, >0.16 in)

Boeing Seminar-7

ETDR Distributed Strain Sensing

Oscilloscope

Step Generator

Incident voltage step Reflected voltage step

Distance between the points ofmonitoring and discontinuity

Z R jL G jC [( ) / ( )] / 1 2

Z: Characteristic ImpedanceR: ResistanceL: InductanceG: ConductivityC: Capacitance

Principle of Electrical Time Domain Reflectometry (ETDR) Distributed Sensing

Fault Detection along a Power Transmission Coaxial Cable Signal Integrity Testing in an Electronic Package

Boeing Seminar-8

Coaxial Cable

Distributed Strain Sensing Mechanism

PVC jacket

tinned copper braid outer conductor

Polyethylene (or Teflon) dielectric

bare copper covered steel inner conductor

F

F

Time

Ref

lect

ion

Coe

ffici

ent

Transverse Shear

F F

Axial Tension

Time

Ref

lect

ion

Coe

ffici

ent

F F

Axial Compression

Time

Ref

lect

ion

Coe

ffici

ent

Boeing Seminar-9

Embedded ETDR Sensor

Strain Measurement

Concrete host material

crack damageCrack Damage Detection

Detection and Measurement of Stress Concentration

Boeing Seminar-10

Concrete Beam with Embedded Commercial RG-174 Coaxial Sensor Subjected to 3-Point Bending

Distance (in)71 81.5 918179.75

-0.012

-0.008

-0.004

0.000

0.004

3.40E-08 3.60E-08 3.80E-08 4.00E-08 4.20E-08 4.40E-08Time (sec)

Ref

lect

ion

Coe

ffic

ient

4 klb-in5 klb-in6 klb-in5.85 klb-in5.6 klb-in2.25 klb-in

Commercial Coaxial Cable

Capture Deformation Shape

Low Signal-to-Noise Ratio

Commercial Coaxial Sensor

Boeing Seminar-11

High Sensitivity ETDR Prototype Sensor

Polyolefin Jacket

Braid Tinned Copper Outer Conductor

Strand Tinned Copper Inner Conductor

Rubber Dielectrics

Outer Diameter ofPolyolefin Jacket

(in)

Outer Diameter ofOuter Conductor

(in)

Outer Diameterof Dielectric

(in)

Diameter ofInner Conductor

(in)

Impedance()

DielectricConstant

Large Cable 0.182 0.1606 0.1395 0.0483 40 2.8983

Small Cable 0.138 0.0985 0.0642 0.0303 40 2.7496

Boeing Seminar-12

Sensitivity Test

Clamp

ETDR Signal Triggering Unit

HP-5412T Digital Oscilloscope

High Sensitivity ETDR Prototype Sensor Subject to a Constant Spring Force of 28 lbs.

Boeing Seminar-13

Sensitivity Test (Cont.)

-0.15

-0.13

-0.11

-0.09

-0.07

-0.05

-0.03

-0.01

0.01

0.03

0.05

1.800E-08 2.200E-08 2.600E-08 3.000E-08 3.400E-08 3.800E-08

Time (sec)

Ref

lect

ion

Coe

ffic

ient

Large Prototype Cable

RG-58/U

ETDR signal sensitivity response of large prototype cable

ETDR signal sensitivity response of small prototype cable

-0.15

-0.13

-0.11

-0.09

-0.07

-0.05

-0.03

-0.01

0.01

0.03

0.05

1.80000E-08 2.20000E-08 2.60000E-08 3.00000E-08 3.40000E-08 3.80000E-08

Time (sec)

Ref

lect

ion

Coe

ffici

ent

Small Prototype Cable

RG174

Boeing Seminar-14

Tension Test

Experimental SetupComparison of ETDR signal response of high sensitivity prototype

cable and commercial RG174 cable subject to axial tension

-2.5

-2

-1.5

-1

-0.5

00 1 2 3 4 5

Strain (%)

Impe

danc

e C

hang

e (

)Prototype Cable

RG-174 Cable

Boeing Seminar-15

Reflection Coefficient

Impedance

)1()1(

1i

iii ZZ

V11

V12

V13

V14

V15

V11R2

V12R3

V13R4

V14R5

V15R6

V21

V22

V23

V24

V25

V31

V32

V33

V34

V35

V31

V41

V42

V43

V44

(1-R2)V12R3

(1-R2)(1-R3)V13R4

(1-R3)V13R4

V''31

V'21

V'22

V'23

V'24

(1-R4)V14R5

(1-R5)V15R6(1-R3)(1-R4)V14R5

(1-R2)(1-R3)(1-R4)V14R5 (1-R4)(1-R5)V15R6

V''32

V''33

V''34

V26V'25

V'26

V16

V17V16R6

V17R7V'41

V'42

V'43

V'44

V'35

])1)( 51443 RVR

V51

V52

V53

V54

V'51

V'52

V'53

Infinite Reflections

1

11,1

1,11

1

11,11,11

)1)(1(11

2

1)1()2(1)1()1(

)1(

))1((

)1()1(

)1(

])1()[()1(

i

jji

iii

i

jjiiii

nmnnmnmn

mn

niimnmnnmnnmnmn

V

VV

VVV

VVV

VVVV

Calibration of ETDR Signal Waveform

Boeing Seminar-16

Bending Response Monitoring of a Concrete Beam

Boeing Seminar-17

Bending Response - Results (Cont.)

ETDR Signal Waveforms

-0.20

-0.15

-0.10

-0.05

0.00

0 3 6 9 12 15 18 21Beam Span (in)

Def

lect

ion

(in)

LVDTETDRLoad (lbs) LVDTETDRLoad (lbs) LVDTETDRLoad (lbs)

314568766962 11661333

314568766962 11661333

Deflection Profile of the Beam

-3

-2

-1

0

22.21 23.21 24.21 25.21 26.21 27.21 28.21

Time (ns)

Impe

danc

e C

hang

e (Ω

)

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0 3 6 9 12 15 18 21

Beam Span (in)

P=314 lb

P=568 lb

P=766 lb

P=962 lb

P=1166 lb

P=1333 lb

Boeing Seminar-18

Damage DetectionETDR Signal Waveforms

Crack Damages

-3

-2

-1

0

22 24 25 27 28

Time (ns)

Impe

danc

e C

hang

e (Ω

)

-1.2

-1

-0.8

-0.6

-0.4

-0.2

0

0 5 10 15 20Beam Span (in)

1392 lbs

1420 lbs

1416 lbs

1441 lbs

1489 lbs

1499 lbs

1528 lbs

Boeing Seminar-19

In the Near Future

Field Application

Dam

Bridge

Landslide

Boeing Seminar-20

Deformation Shape Measurement

Structural Integrity Monitoring

Large Flexible Aerospace Structures

Boeing Seminar-21

Shape Measurement of Large Structure

Wooden Beam (1.5x0.2x72 in.)with Surface-Bonded High Sensitivity Prototype Cable

Experimental Setup

Fixture

ETDR Signal Triggering Unit

High Sensitivity ETDR Prototype Cable

Boeing Seminar-22

Shape Measurement of Large Structure (Cont.)

ETDR Signal Response of the Prototype Sensor

1st Mode Bending

-0.014

-0.012

-0.010

-0.008

-0.006

-0.004

-0.002

0.000

0.002

0.004

2.50E-08 3.00E-08 3.50E-08 4.00E-08 4.50E-08 5.00E-08 5.50E-08

Time (s)

Ref

lect

ion

Coe

ffici

ent

ETDR Signal

Trendline

Boeing Seminar-23

ETDR Signal Response of the Prototype Sensor

2nd Mode Bending

-0.014

-0.012

-0.010

-0.008

-0.006

-0.004

-0.002

0.000

0.002

0.004

2.50E-08 3.00E-08 3.50E-08 4.00E-08 4.50E-08 5.00E-08 5.50E-08

Time (s)

Ref

lect

ion

Coe

ffici

ent

ETDR Signal

Trendline

Shape Measurement of Large Structure (Cont.)

Boeing Seminar-24

ETDR Signal Response of the Prototype Sensor

1st Mode Reverse Bending

-0.014

-0.012

-0.010

-0.008

-0.006

-0.004

-0.002

0.000

0.002

0.004

2.50E-08 3.00E-08 3.50E-08 4.00E-08 4.50E-08 5.00E-08 5.50E-08

Time (s)

Ref

lect

ion

Coe

ffici

ent

ETDR Signal

Trendline

Shape Measurement of Large Structure (Cont.)

Boeing Seminar-25

ETDR Signal Response of the Prototype Sensor

2nd Mode Reverse Bending

-0.014

-0.012

-0.010

-0.008

-0.006

-0.004

-0.002

0.000

0.002

0.004

0.006

0.008

0.010

0.012

0.014

2.50E-08 3.00E-08 3.50E-08 4.00E-08 4.50E-08 5.00E-08 5.50E-08

Time (s)

Ref

lect

ion

Coe

ffici

ent

ETDR Signal

Trendline

Shape Measurement of Large Structure (Cont.)

Boeing Seminar-26

ETDR Film Sensor

This image cannot currently be displayed.

ETDR film sensor

To ETDR instrumentation

Laminated Composites

ETDR Film Sensor

22 in

0.5 in

Polymer FilmProtective Coating

Silver Print

110 m

Envisioned Composite Laminate with Embedded ETDR Film Sensor

Boeing Seminar-27

Impedance-Based Piezoelectric SensorHealth Monitoring and Damage Detection

•Bolted Structural Components•Adhesively Bonded Substructures•Riveted Substructures•Composite Panels (Delamination)•Engine Turbine Blades (Crack Damage)

Go, No Go ?

• Off-Duty Aircraft

• Stockpile Missile

Need Active Sensor to Interrogate the Structure

Boeing Seminar-28

Piezoelectric Sensor Piezoelectric Materials

(Two-Way Fully Coupled Electromechanical Property)

v = V sin(t) m

c

k

PZT

i = I sin(t+)

Piezo sensors convert force and motion to voltage and charge

Piezo actuators convert voltage and charge to force and motion

out

in

iv

out

in

Current) (SensingVoltage) (Actuating Impedance

Boeing Seminar-29

Damage Detection ExperimentBolt-Jointed Aluminum Cantilever Beam

200Unit: mm

Thickness of the Beam =1.7

32

48

32

48

32

ClampedAluminum BeamPiezoelectric Sensor

Experimental Set-Up

Piezoelectric Sensor

Aluminum Beam Bolt FastenerImpedance Analyzer

Tight Joint: 1 N-m Loose Joint: 0.1 N-m

Boeing Seminar-30

Experimental ResultsRepeatability Test for “Healthy” Joint (All 9 Bolts were Tightened)

0

1000

2000

3000

4000

5000

3.5 4.2 4.9 5.6 6.3 7

Frequency (KHz)

Impe

danc

e A

mpl

itude

(Ohm

s)

Test # 1

Test # 2

Test # 3

Test # 4

Boeing Seminar-31

Experimental Results (cont.)Repeatability Test for “Healthy Joint” Reference Baseline

0

1000

2000

3000

4000

5000

3.5 4.2 4.9 5.6 6.3 7

Frequency (KHz)

Impe

danc

e A

mpl

itude

(Ohm

)

All 9 Bolts Tightened

1st Bolt Loosen and Retightened

2nd Bolt Loosen and Retightened

3rd Bolt Loosen and Retightened

4th Bolt Loosen and Retightened

5th Bolt Loosen and Retightened

6th Bolt Loosen and Retightened

7th Bolt Loosen and Retightened

8th Bolt Loosen and Retightened

9th Bolt Loosen and Retightened

Boeing Seminar-32

Experimental Results (cont.)Damage Detection: 1st Bolt Loosen

0

1000

2000

3000

4000

5000

3.5 4.2 4.9 5.6 6.3 7

Frequency (KHz)

Impe

danc

e A

mpl

itude

(Ohm

)

Healthy

1st Bolt Loosen

Boeing Seminar-33

Experimental Results (cont.)Damage Detection: 1st Bolt Loosen Repeated

0

1000

2000

3000

4000

5000

3.5 4.2 4.9 5.6 6.3 7

Frequency (KHz)

Impe

danc

e A

mpl

itude

(Ohm

)

Healthy

1st Bolt Loosen

1st Bolt Loosen Repeated

Boeing Seminar-34

Experimental Results (cont.)Damage Detection: with Increasing Number of Loose Bolts

0

1000

2000

3000

4000

5000

3.5 4 4.5 5 5.5 6 6.5 7

Frequency (KHz)

Impe

danc

e (O

hm)

Healthy

One bolts loosen

Two bolts loosen

Threer bolts loosen

Four bolts loosen

Five bolts loosen

Six bolts loosen

Seven bolts loosen

Eight bolts loosen

Nine bolts loosen

Boeing Seminar-35

Experimental Results (cont.)Frequency Variation on Even Numbered Modes

3

3.5

4

4.5

5

5.5

6

6.5

7

0 1 2 3 4 5 6 7 8 9

Number of Loose Bolts

Res

onan

ce F

requ

ency

(KH

z)

S th mode S+2 th mode S+4 th mode S+6 th mode

Boeing Seminar-36

Finite Element SimulationFE Model

8-Node 3D Coupled-Field Piezoelectric Element with Ux, Uy, Uz, and V Nodal DoF

8-Node 3D Structural Brick Element with Ux, Uy, and Uz Nodal DoF2-Node 3D Structural

Spar Element with Ux, Uy, and Uz Nodal DoF

Aluminum Beam 1 Aluminum Beam 2

Piezoceramic Sensor

Harmonic Response Analysis -> Applied Load: Nodal Voltage, Vosin(t)Output: Nodal Charge

Boeing Seminar-37

Piezoelectric Constitutive Equation

jijjkijki

mmijklijklij

EeqEeD

ij stress tensorij strain tensor Ei electric field vector qi electric flux density vector Dijkl elastic stiffness tensor (evaluated at constant electric field)ij dielectric tensor (evaluated at constant mechanical strain)

lmjkilmijk Dde piezoelectric stress coefficient tensor ilmd piezoelectric strain coefficient tensor.

Boeing Seminar-38

FEA-Experiment ComparisonImpedance Spectrum of the Healthy Joint

0

1000

2000

3000

4000

5000

3.5 4 4.5 5 5.5 6 6.5 7

Frequency (KHz)

Impe

danc

e (O

hm)

FEA

Experiment

Boeing Seminar-39

Hybrid Linear/Rotary Stepper Motor (Cont.)

Rotary Driver (at disengaged

position)

Linear Driver

y

z

x

z

Linear Driver

Rotary Driver (at disengaged

position)

1 3 1 3 1 3 1 31 3

2 42 42 42 42 4

Power-Off Position Step 1 Step 2 Step 3 Step 4

Boeing Seminar-40

Hybrid Linear/Rotary Stepper Motor (Cont.)

2

1

3

42

1

3

4

Step 2 Step 3 Step 4

2

1

3

4

Core RodCore Rod

Core RodCore Rod

2

Actuator 1

Actuator 3

4

Step 1Power-Off Position

2

1

3

4

Core Rod

Boeing Seminar-41

Concept DemonstrationMotor Assembly

Normal Mode PZT actuator

Aluminum motor core shaft (0.5”x0.5”x6”)

Aluminum retaining wall

Plexiglas insulating shoe

Shear Mode PZT actuator d33 mode element

d15 mode element

glass insulation shoe

-2000

-1500

-1000

-500

0

500

1000

0 5 10 15 20 25 30

Time (sec.)

Vol

tage

(v)

V3 V1

V3' V1'

Driving Signal

Multi-channel filter

PC based multi-channelfunction generator

Driver 1PZT element d31 griping

Driver 1PZT element

d15 shear

Driver 2PZT element d31 griping

Driver 2PZT element

d15 shear

HV amplifier HV amplifier HV amplifier HV amplifier

Boeing Seminar-42

It Moved!

-25

-20

-15

-10

-5

0

5

10

15

20

25

0 0.2 0.4 0.6 0.8 1

Time (sec.)

Dis

plac

emen

t (m

)

1 Hz

3 Hz

5 Hz

10 Hz

20 Hz

forward motion

backward motion

Driving Frequency (Hz) 1 3 5 10 20

Motor Core Velocity (m/s) 1.2 3.8 6.8 12.4 21.8

Boeing Seminar-43

Shape Memory Alloy (Nitinol) Actuator

• Variable Structural Stiffness for Natural Mode Tuning to Avoid Flutter

• Active Shape Control to Improve Aeroelastic Effectiveness

Shape Memory Alloy (SMA)

Boeing Seminar-44

Adaptive Stress Alleviation of Pressure Vessel

SMA Hybrid Composites Pressure Vessel

Composite cylinder with a layer of SMA actuator

Activation of the SMA layer induces shrinkage against the cylinder

The induced pressure by the SMA layer creates the compound cylinder effect, resulting in structural stress alleviation on the composite cylinder

SMA ActuatorComposite Pressure Vessel

Boeing Seminar-45

0

30

60

90

120

150

50 100 150 200 250 300

Activation Temperature (°F)

Hoo

p St

ress

(ksi

)

R = 0.005

R = 0.495

R = 0.505

R = 0.995

• Significant stress alleviation can be achieved on a graphite/epoxy pressure vessel with a 1.5% recoverable prestrain of the SMA actuator

Hoop Stress at Various Locations along the Cylinder Walla Function of Activation Temperature of the SMA

Adaptive Stress Alleviation of Pressure Vessel

Boeing Seminar-46

Smart Materials & Structures

We cannot create life,

but can learn from life

to save life.

Boeing Seminar-47

FEA of a Solar Sail Membrane

pp

circular membrane d = 10 m thickness = 7.6 microns partially illuminated light pressure with

an oblique incident angle of 35

Induced radial displacement contourInduced radial stress contour

Boeing Seminar-48

FEA Modeling of a Spindle Lug

Boeing Seminar-49

Background

Crack failure occurred on the trailing lower lug

Crack damage appears to initiate at the bushing/lug interface

Fatigue and possibly fretting fatigue origins were SEM observed

No root cause for the premature failure has been identified

Boeing Seminar-50

FE Static Analysis

FEA Constraint and Load Conditions

70,000 lbs total load applied Surface Pressure

Boeing Seminar-51

FEA Results

Tension Load = 29,000 lb , P = 3,200 psi

Principal Stress Contour Von Mises Contour

Boeing Seminar-52

Indoor(Controlled Climate)

Outdoor(Changing Climate) Concrete

(Porous)

FRP (Permeable)

Hygrothermal Stress and Moisture Damage at the Interface -> Delamination

Unreinforced Masonry Wall with FRP Reinforcement Upgrade

FEA Modeling of Hygro-Thermo-Mechanical Response of a Fiber Reinforced Polymer Composites Reinforcement

Boeing Seminar-53

Heat and Moisture Transport Model

h Relative humidity of the ambient air (dimensionless)

Vapor resistivity of the media (dimensionless)

p Vapor permeability of the air (kg/m s Pa)

Ps Saturation vapor pressure (Pa)

ASTM version (2001)

)]([)( sP hPD

t

)]([)( sP

v hPhTtTc

All parameters are well defined and physically measurable.

Boeing Seminar-54

Finite Element Modeling Finite element formulation in terms of nodal values

ee

ee

e

ee Q

Th

DTh

C

][][ **

where: ),,( zyxN = vector of shape functions

e

e

Th

= nodal humidty/temperature vector

dVBDBDV

Te ][][][][ ** element humidity and heat diffusion matrix

dVNN

cC

C T

Ve 00

][ *

* element humidity and heat capacity matrix

dSqNQSe

* element boundary humidity and heat flux

TNLB ][

0* Th DD

D = Humidity and heat diffusion matrix

The Finite element formulation is implemented in FEMLAB computer software.

Boeing Seminar-55

Case Study: Results

Transient relative humidity profile for Tout=40oC at Tin=20oC along the centerline at X=198 mm

40

50

60

70

80

90

100

0 3.88 7.76 11.64 15.52 19.4 23.28 27.16 31.04 34.92 38.8X (mm)

Rel

ativ

e H

umid

ity (%

)

40

50

60

70

80

90

100-194 -155.2 -116.4 -77.6 -38.8 0 38.8 77.6 116.4 155.2 194

1 day 5 days 20 days 1 month 2 months

3 months 5 months 10 months Steady State

FRP Concrete

Boeing Seminar-56

Hygro-Thermally Induced Interfacial StressesFinite Element Formulation

thermalswellingtotalelastic DD T

refrefrefthermal TTTTTT 000)()()( 321

where:i the thermal expansion coefficients

in the principle material directions i = 1,2,3

refT = the reference (strain-free) temperature

wvu

LTxzzyzxyzyxtotal

T

xyz

zxy

zyx

L

000

000

000

Trefrefrefswelling 000)()()( 321

Boeing Seminar-57

Finite Element Formulation swellingthermalSB FFFFUK ][

where:

Trrr wvuwvuwvuU ...222111 = nodal displacement vector

dVBDBKV

T ][][][][ = element stiffness matrix

dVFNF bV

TB ][ = element body force vector

dSFNF sS

TS ][ = element force due to the surface loading

dVDBF thermalV

Tthermal ][][ = element force vector due to the thermal expansion

dVDBF swellingV

Tswelling ][][ = element force vector due to the moisture swelling

TNLB ][

T

r

r

r

NNNNNN

NNNzyxN

00...000000...000000...0000

),,(

21

21

21

= shape function matrix

The Finite element formulation is implemented in FEMLAB computer software.

Boeing Seminar-58

-100

0

100

200

300

400

500

600

40 60 80 100 120 140 160 180 200

Z (mm)

Szy

(kPa

)

Tout = 10o C

Tout = 20o C

Tout = 40o C

Tout = 60o C

FEA ResultsInterfacial shear stress, yz, distribution for various outdoor temperatures along the z-axis

at x = 198 mm in FRP laminate

Boeing Seminar-59

-400

-200

0

200

400

600

800

1000

1200

198 208 218 228 238 248 258 268 278 288 298 308 318

X (mm)

y (k

Pa)

Tout = 10o C

Tout = 20o C

Tout = 40o C

Tout = 60o C

FEA Results (cont.)Peeling stress, y, distribution for various outdoor temperatures along the z-axis at

x = 198 mm in FRP laminate